In odontotherapy, a region of the surface of a patient's jaw (including a maxilla, a mandible, a temporomandibular joint, and a maxillary sinus) may be imaged as one panoramic radiograph (hereinafter simply referred to as a panoramic image). The panoramic image is used as reference information beneficial for judging whether major diseases in the dental field are present or not and for determining, for example, other treatment policies. In particular, advancements in improved performance, downsizing, reduced cost, and similar improvement of an X-ray imaging apparatus and a digital information apparatus have been made recently. Accordingly, dental clinics that introduce an imaging apparatus for taking a digital panoramic image have been increasing.
A taken panoramic image is stored in, for example, an electronic medical recording system as image data together with basic information of a patient and medical information of the patient. The basic information includes, for example, a name, a date of birth, and a gender of the patient. The medical information includes, for example, treatment history up to the present and any other disease history. This facilitates checking a content of treatment of the patient after a set of treatment has been completed and grasping a healed state of the patient. The panoramic image may include information beneficial for diagnosing systemic diseases as well as diseases in the dental field. Accordingly, a technique for providing the beneficial information from the panoramic image including a mandible region has been developed (for example, see Patent document 1 to Patent document 3).
To describe more specifically, the taken panoramic image includes a pair of maxillary sinuses regions, which are one among the paranasal sinus pairs located on the right and left of the nose. The maxillary sinus has a bottom portion close to a tooth root portion. Therefore, bacteria causing an odontopathy, such as a decayed tooth and a periodontal disease, at a back tooth on a maxilla side may invade the maxillary sinus regions. This may result in incidence of “odontogenic maxillary sinusitis.” This odontogenic maxillary sinusitis needs to be treated together with a tooth causing the odontogenic maxillary sinusitis, such as a decayed tooth, and therefore is generally treated at a dental clinic.
The panoramic image of a patient who has been affected by odontogenic maxillary sinusitis has the following features. That is, among a pair of maxillary sinuses at the right and left of a nose placing the nose as the center, one maxillary sinus region (the affected region) is radiopaque. Therefore, the affected region is mainly drawn in white or bright colors. The other maxillary sinus region (the normal region) is radiolucent. Therefore, the normal region is drawn in black or dark colors. That is, when the densities of the drawn right and left maxillary sinus regions are remarkably different in the panoramic image including both maxillary sinuses regions, this suggests high possibility of being affected by odontogenic maxillary sinusitis. Different from “odontogenic” maxillary sinusitis, in the case of “rhinogenous” maxillary sinusitis or “hematogenous” maxillary sinusitis, the distinctive observation (the difference in densities of the drawn right and left maxillary sinus regions) is less likely to be shown.
Meanwhile, the inventors of this application have developed an image processing system that emphasizes difference in density in the right and left maxillary sinus regions included in the taken panoramic image. The inventors of this application have also developed a system that creates a difference image of the right and left maxillary sinus regions (see Non-Patent Document 1). Use of this system allows a dentist or similar person to easily recognize density difference in the right and left maxillary sinus regions based on the contralateral subtraction image. As a result, since the dentist or similar person can judge possibility of whether a patient is affected by maxillary sinusitis and, for example, then examine the patient closely, early diagnosis and early treatment of odontogenic maxillary sinusitis are possible.
Here, technologies (atlases) for estimating the location where a specific target area is present from an obtained medical image based on prior information have been numerously developed. Disclosure examples of the technologies (atlases) are as follows. Namely, methods for creating an atlas for the brain region (see Non-Patent Document 2 and Non-Patent Document 3), methods for creating an atlas for the abdominal organs, whose morphological differences among individuals are greater than those of the brain region (see Non-Patent Document 4 and Non-Patent Document 5), and technology that estimates a degree of similarity between images using mutual information and create an atlas using only an image with high similarity (for example, Non-Patent Document 6) are disclosed. With these technologies, numerous attempts to create atlases in order to specify the target position from the medical image such as a panoramic image have been made. These techniques are effective techniques to judge possibility of odontogenic maxillary sinusitis and to specify a region of maxillary sinus.